Capillaria aerophila is a nematode parasite found in the respiratory tract of foxes,[1] dogs,[2] and various other carnivorous mammals.

However, secondary bacterial infections of the respiratory tract, including pneumonia, may develop in heavy infestations.

[5] Capillaria aerophila has been found on every continent, and occurs in dogs, cats, and a wide range of wild mammals.

When a suitable host eats these mature eggs, the larvae hatch in the intestines and migrate to the lungs.

Reported infestation rates in dogs and cats which are kept as pets in Europe and North America are generally less than 10%.

These developments are usually characterized by a whistling sound when the animal breathes, frequent sneezing, or a deep, wheezing cough.

Most reports of C. aerophila in wildlife are simply parasite field surveys, and do not mention specific symptoms.